[lvc-project] [PATCH] drm/amdgpu: fix NULL dereference in gfx_v9_0_kcq() and kiq_init_queue()

[Alex Deucher]

On Sat, May 24, 2025 at 2:14 AM Alexey Nepomnyashih <sdl at nppct.ru> wrote:
>
> A potential NULL pointer dereference may occur when accessing
> tmp_mqd->cp_hqd_pq_control without verifying that tmp_mqd is non-NULL.
> This may happen if mqd_backup[mqd_idx] is unexpectedly NULL.
>
> Although a NULL check for mqd_backup[mqd_idx] existed previously, it was
> moved to a position after the dereference in a recent commit, which
> renders it ineffective.

I don't think it's possible for mqd_backup to be NULL at this point.
We would have failed earlier in init if the mqd backup allocation
failed.

Alex

>
> Add an explicit NULL check for tmp_mqd before dereferencing its members.
>
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>
> Cc: stable at vger.kernel.org # v5.13+
> Fixes: a330b52a9e59 ("drm/amdgpu: Init the cp MQD if it's not be initialized before")
> Signed-off-by: Alexey Nepomnyashih <sdl at nppct.ru>
> ---
>  drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> index d7db4cb907ae..134cab16a00d 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> @@ -3817,10 +3817,9 @@ static int gfx_v9_0_kiq_init_queue(struct amdgpu_ring *ring)
>          * check mqd->cp_hqd_pq_control since this value should not be 0
>          */
>         tmp_mqd = (struct v9_mqd *)adev->gfx.kiq[0].mqd_backup;
> -       if (amdgpu_in_reset(adev) && tmp_mqd->cp_hqd_pq_control){
> +       if (amdgpu_in_reset(adev) && tmp_mqd && tmp_mqd->cp_hqd_pq_control) {
>                 /* for GPU_RESET case , reset MQD to a clean status */
> -               if (adev->gfx.kiq[0].mqd_backup)
> -                       memcpy(mqd, adev->gfx.kiq[0].mqd_backup, sizeof(struct v9_mqd_allocation));
> +               memcpy(mqd, adev->gfx.kiq[0].mqd_backup, sizeof(struct v9_mqd_allocation));
>
>                 /* reset ring buffer */
>                 ring->wptr = 0;
> @@ -3863,7 +3862,7 @@ static int gfx_v9_0_kcq_init_queue(struct amdgpu_ring *ring, bool restore)
>          */
>         tmp_mqd = (struct v9_mqd *)adev->gfx.mec.mqd_backup[mqd_idx];
>
> -       if (!restore && (!tmp_mqd->cp_hqd_pq_control ||
> +       if (!restore && tmp_mqd && (!tmp_mqd->cp_hqd_pq_control ||
>             (!amdgpu_in_reset(adev) && !adev->in_suspend))) {
>                 memset((void *)mqd, 0, sizeof(struct v9_mqd_allocation));
>                 ((struct v9_mqd_allocation *)mqd)->dynamic_cu_mask = 0xFFFFFFFF;
> @@ -3874,8 +3873,7 @@ static int gfx_v9_0_kcq_init_queue(struct amdgpu_ring *ring, bool restore)
>                 soc15_grbm_select(adev, 0, 0, 0, 0, 0);
>                 mutex_unlock(&adev->srbm_mutex);
>
> -               if (adev->gfx.mec.mqd_backup[mqd_idx])
> -                       memcpy(adev->gfx.mec.mqd_backup[mqd_idx], mqd, sizeof(struct v9_mqd_allocation));
> +               memcpy(adev->gfx.mec.mqd_backup[mqd_idx], mqd, sizeof(struct v9_mqd_allocation));
>         } else {
>                 /* restore MQD to a clean status */
>                 if (adev->gfx.mec.mqd_backup[mqd_idx])
> --
> 2.43.0
>